Study of Caustification from Produced Red Mud in Alumina Production Process by Bayer Method

Sodium hydroxide reacts with silica and other components in bouxite to form hydro aluminum silicate sodium which is in the form of red mud in alumina production process. The objective of caustification process is recovery of Na2O in the form of caustic from sodium salts because of reduction in alkali losses within alumina production process.One of the methods for Na2O recovery is to use Ca(OH)2 in process of red mud washing where Ca is replaced with Na in solution. The chosen red mud is selected from the red mud washing unit in Jajarm Alumina Plant to study effectiveness of different parameters in caustification process.In this study, at first caustification reaction is considered then the effect of some parameters such as time, amount of added lime and its’ type in caustification process are investigated. Experiments are carried out at atmospheric pressure. Experiences have shown that experiments should be conducted at a temperature above 90 ºC, to have a successful reaction. It this study, it is found that a contact or reaction time of 4-6 hrs is optimum. According the results, 2.5~3.5 time period are the best for different ratios of lime to caustic.